Historically, avocado scion varieties were propagated by grafting them over seedling rootstocks of three origins: Mexican, Guatemalan and West Indian. Each growing area used the alternative best suited to its proper ecologic conditions. California chose seedling rootstocks of Mexican origin, typically ‘Topa Topa’ (unpatented). Florida chose seedling rootstocks of West Indian origin, typically ‘Waldin’ (unpatented). Seedling rootstocks proved to be variable in their morphological and productive characteristics. The avocado industry demanded more uniformity in growth and productivity of orchard trees than trees on seedling rootstocks were able to provide.
The search for an answer led to the development of clonal rootstocks where all trees in an orchard were genetically identical to each other. Eventually, ‘Duke 7’ (unpatented) became the leading clonal avocado rootstock for California. This clonal rootstock, and more recently also the ‘Merensky 2’ (U.S. Plant Pat. No. 15,309) clonal rootstock, have been introduced for cultivation worldwide. Clonal avocado rootstocks, like seedling avocado rootstocks, are not necessarily best suited to the particular soil-water-climate conditions of all avocado growing regions world-wide.
Currently, the main avocado variety grown in the word is ‘Hass’ (U.S. Plant Pat. No. 139, the contents of which are incorporated herein by reference). The main markets have year-round supply of ‘Hass’ avocados and end consumers are very used to buying ‘Hass’. Many other avocado varieties have been created and patented in the last twenty years, but none of them has been able to obtain important interest from growers. The main reason for the lack of interest is that the market still prefers ‘Hass’.